Altair-viz：有没有办法改变多面图表的显示顺序？

Question

I want to facet my plot by column (straight-forward enough), but the faceted sub-plots are displayed in alphabetical order and I would like them displayed in a custom order. Using this example from the Altair website facets by species and displays the sub-plots in alphabetical order: 'setosa', 'versicolor', 'virginica'.

import altair as alt
from altair.expr import datum
from vega_datasets import data
iris = data.iris.url

alt.Chart(iris).mark_point().encode(
    x='petalLength:Q',
    y='petalWidth:Q',
    color='species:N',
    column='species:N'
).properties(
    width=180,
    height=180
)

Is it possible to have this example display as: 'versicolor', 'virginica', 'setosa'? Thanks.

Answer 1

You can use the sort property of the column encoding. For example:

import altair as alt
from altair.expr import datum
from vega_datasets import data
iris = data.iris.url

alt.Chart(iris).mark_point().encode(
    x='petalLength:Q',
    y='petalWidth:Q',
    color='species:N',
    column=alt.Column('species:N', sort=['virginica', 'setosa', 'versicolor'])
).properties(
    width=180,
    height=180
)